1. Field
The following description relates to an optical communications network, and particularly to an apparatus and method for registering and de-registering an optical network unit (ONU).
2. Description of the Related Art
Recently, as optical communications technology is quickly being developed, an optical line terminal (OLT) in an optical network can enhance operation efficiency of network infrastructure by controlling and managing not the network resources in one dimension of each time and wavelength but the network resources in multiple dimensions where at least two of time, wavelength, frequency, code, and space are combined. For example, for such a purpose, resources allocation of two-dimensional networks is studied recently, such as a time- and wavelength-division multiplexing passive optical network (TWDM-PON) and an orthogonal frequency-division multiple access (OFDMA)-PON.
Each ONU connected to the OLT for control and management of network resources in the multi-dimension is required to be registered to an optical network or de-registered depending on the need. Here, the registration indicates joining the ONU that is newly connected or inactive in the optical communications network or resuming operations. The de-registration indicates an inactivation of the operating ONU.
In the past, only the technologies for the OLT to register and de-register the ONU by using a single channel are provided when the OLT communicates with the ONU through the single channel in an optical communications network.
The related art 1 (Sumitomo Electric Industries, Ltd., “a registration method of a PON system and terminal”, Application No. KR10-2008-7023635, Pub. No. KR10-2008-0114768, Pub. Date: Dec. 31, 2008) discloses a method of registering an ONU at the lowest transmission speed when being performed at various types of the transmission speeds in a single channel.
The related art 2 (OKI Electric Industry Co., Ltd., Tokyo (JP), “Optical network unit registration method,” U.S. application Ser. No. 13/789,886, Pub. No. US2013/0259482A1, Pub. Date: Oct. 3, 2013.) discloses a method of performing a registration process for each wavelength by opening the synchronized discovery window when a plurality of optical branches connected to a plurality of ONUs is connected, with one optical routing unit, to a plurality of OLTs that has each single channel.
The data transmission time according to the distance between the OLT and the ONU is measured through a ranging process after the registration process. To register and de-register the ONU, the OLT receives responses from the ONU by opening a contention window of a predetermined size because it is hard to precisely estimate the responses from the ONU that is located at a specific distance. While the contention window is opened, the data transmission of the operating ONU is not allowable. The round-trip time (RTT) of 200 us is required at an existing transmission distance of 20 km, but in the case of long distance transmission, the RTT of 1 ms is required, thereby stopping the data transmission during at least the RTT and causing problems in providing a low-latency service. In the case of the registration, since the OLT does not have information on the ONU that is newly connected thereto, the OLT need to open the contention window during the time of the contention window as much as the maximum acceptable distance to the ONU. Here, if a single channel is used for the registration, the service may be often disconnected.
In addition, since, in the existing manner, since the resources are wasted for the increased RTT, increasing the scale of the time of the contention window may reduce the collision during the contention in practice. However, during the increased scale of the time of the contention window, data cannot be transmitted, thereby being inefficient in terms of the network resources.